What you say makes sense for the screening rounds - resume shortlisting and a phone screen. These are centered around rejecting candidates. But face to face interviews are supposed to be the other way. As far as I know, Google asks for the GPA mostly towards the end. That doesn't save them any time. It shows they care about academics.

On a general note, is there any company that tries to extract patterns out of their employees performance track records; like a feedback loop into their interview process?